Three distinct classes of single-cell clones were derived from the B16 mouse melanoma: (1) "null" clones produce tumors in syngeeic C57BL/6 mice but form few or no lung colonies followong injection into the tail vein and fial to metastasize; (2) colonizing clones from numerous lung colonioes following intravenous injection but do not metastasize significantly; and (3) metastatic clones spontaneously metastasize to the lungs but are inefficient at forming lung colonies when injected in the tail vein. Utilizing representative clones, the basis for distinction between tumorigenicity, lung colonization, and lung metastasis will be probed, to provide novel information about the occurrence and apparent specific organ tropism of spontaneous metastasis. The capacity of tumor cells growing subcutaneously to invade into, and circulate within, blood vessles will be monitored by vasular perfusion an characterization of collected cells, and by histopahtological examination. The ability of cells from subcutaneous growths or intravenously injected cells to arrest, extravasate, and proliferate in organ parenchyma will be assessed similarly and by measuring survival kinetics of radiolabeled cells, interaction of cells with host lymphocytes and platelets, invasiveness through chick chorioallantoic membrane, shedding of immunogenic surface molecules, and specificity of organ tropism (homing to ectopically implanted organ fragments). The role of unique cell surface antigens related to murine leukemia virus gp70 (B16-gp70, B16-gp80, and B16-gp85), and of host immunity to these antigens, in metastasis and colonization will be investigated in similar fashion, to determine how specific host immunity can influence metastasis. Preliminary studies indicate that the host recognized only these antigents on B16 melanoma cells and that resultant immunity can stimulate metastsis. The ultimate goal of this research is to provide information to permit the designing of successful immunotherapy of metastatic tumors.